1. Field of the Invention setting of virtual connection (VC) in an asynchronous transfer mode (ATM) communication system. More specifically, the invention relates to a VC setting system for a local area network (LAN) communication.
2. Description of the Related Art
An ATM communication system employing a fixed length cell as a transfer unit has an excellent characteristics permitting uniting point-to-multipoint communications and multi-media communications. Therefore, in recent years, the ATM communication system is attracting attention in the application for LAN communication. Here, in burst communication, original information, i.e. service data unit (variable length) is transmitted by dividing into fixed length cells including 5 octets of header and 48 octets of payload, as shown in FIG. 8. Routing in the ATM system is performed using a virtual connection ID (VCI) in the header.
In an ATM communication system, there are two VC setting systems, i.e. a method for setting the VC employing a dedicated VC for signaling setting and a permanent virtual connection (PVC) for semi-permanently setting the VC.
The former method employs a similar method to call setting in an integrated service digital network (ISDN), namely, C (control)-plane and U (User)-plane are set separately and the call in U-plane communication is set by C-plane, which method is referred to as "outband signaling".
On the other hand, the later method does not employ C-plane, in which routes for all distant users are preliminarily established for selecting VC depending upon the distant user to call.
The PVC method has been disclosed in Japanese Unexamined Patent Publications Nos. 2-234538, 1-144745, 1-126043, 2-239749, 2-284543 and 3-97334.
In the former method employing outband signaling, the following drawback can be encountered. Namely, the communication in C-plane is a communication not with the distant user but with a call control portion. In case of communication between users with small data amount, the data amount to be handled by U-plane becomes substantially equal to the data amount to be handled by C-plane to cause large overhead resulting in increasing of the delay period and degradation of throughput.
On the other band, in the later technology, namely the method to preliminarily set routes for all distant users, a defect is encountered in the limitation of capacity for setting depending upon bit length of VC. For instance, in case of 16 bits VC, the maximum number of routes is limited at approximately 64000.
In addition, the later PVC method has a shortcoming that a routing table for defining correspondence between VCI and address information has to be preliminarily prepared upon establishing the system. Furthermore, preparation of the routing table requires complicated operation and possibly causes error.